﻿15 
  

   Chapter 
  IV. 
  — 
  The 
  marine, 
  estuarine, 
  and 
  fluviatile 
  alluvia. 
  

   It 
  is 
  not 
  possible 
  to 
  draw 
  definite 
  boundaries 
  between 
  these 
  several 
  

   varieties 
  of 
  alluvium 
  where 
  they 
  come 
  in 
  contact, 
  but 
  their 
  proper 
  

   positions 
  relatively 
  to 
  each 
  other 
  may 
  be 
  easily 
  explained. 
  

  

  The 
  marine 
  and 
  estuarine 
  beds 
  occur 
  intercalated 
  with 
  each 
  other 
  

   along 
  the 
  coast^while 
  the 
  true 
  fluviatile 
  alluvia 
  occupy 
  the 
  valleys 
  of 
  the 
  

   larger 
  rivers 
  which 
  traverse 
  the 
  Madras 
  District, 
  and 
  appear 
  to 
  overlap 
  

   the 
  marine 
  and 
  estuarine 
  beds 
  near 
  the 
  present 
  mouths 
  of 
  those 
  rivers. 
  

  

  The 
  marine 
  and 
  estuarine 
  alluvia 
  occur 
  in 
  a 
  narrow 
  belt 
  running 
  

  

  Deep 
  bay 
  of 
  alluvium 
  * 
  lon 
  S 
  the 
  COast 
  ' 
  and 
  varying 
  ™ 
  width, 
  southward 
  

  

  west 
  of 
  Poouamallee. 
  of 
  g 
  t< 
  Thome, 
  from 
  one 
  to 
  five 
  miles. 
  West 
  of 
  St. 
  

  

  Thome 
  the 
  alluvial 
  belt 
  widens 
  greatly, 
  running 
  up 
  in 
  a 
  deep 
  bay 
  to 
  

  

  beyond 
  Poonamallee 
  cantonment, 
  and 
  there 
  meeting 
  the 
  river 
  alluvium 
  by 
  

  

  which 
  the 
  marine 
  beds 
  appear 
  to 
  be 
  overlaid. 
  Unfortunately 
  no 
  sections 
  

  

  were 
  found 
  by 
  which 
  to 
  determine 
  exactly 
  the 
  westward 
  limit 
  of 
  

  

  the 
  marine 
  formations. 
  To 
  the 
  north-west 
  by 
  west 
  of 
  Madras 
  (Black 
  

  

  Town) 
  this 
  alluvial 
  bay 
  is 
  bounded 
  by 
  the 
  lateritic 
  beds 
  forming 
  the 
  

  

  so-called 
  Red 
  Hills, 
  and 
  the 
  belt 
  of 
  alluvium 
  narrows 
  to 
  about 
  six 
  

  

  „.,-,-,. 
  * 
  r, 
  miles 
  > 
  *"it 
  immediately 
  to 
  the 
  north 
  it 
  as-ain 
  

   Alluvial 
  delta 
  of 
  Cor- 
  => 
  

  

  teliar 
  and 
  Narnaveram 
  widens 
  out 
  and 
  attains 
  its 
  maximum 
  width 
  in 
  the 
  

  

  rivers. 
  

  

  delta 
  of 
  the 
  Corteliar 
  and 
  Narnaveram 
  rivers. 
  

  

  Here, 
  as 
  in 
  the 
  Poonamallee 
  alluvial 
  bay, 
  there 
  were 
  no 
  section's 
  to 
  

  

  show 
  the 
  westward 
  extent 
  of 
  the 
  marine 
  and 
  estuarine 
  beds. 
  The 
  

  

  northern 
  boundary 
  of 
  this 
  delta 
  extends 
  north-eastward 
  up 
  to 
  the 
  southern 
  

  

  end 
  of 
  the 
  Pulicat 
  lake, 
  where 
  the 
  alluvium 
  measures 
  six 
  miles 
  in 
  

  

  width. 
  A 
  very 
  narrow 
  belt 
  of 
  mixed 
  estuarine 
  and 
  fluviatile 
  alluvium 
  

  

  stretches 
  up 
  the 
  south-west 
  side 
  of 
  the 
  lake, 
  while 
  its 
  bed 
  and 
  the 
  

  

  islands 
  by 
  which 
  it 
  is 
  cut 
  off 
  from 
  the 
  sea 
  consist 
  of 
  marine 
  and 
  estuarine 
  

  

  deposits. 
  The 
  outer 
  or 
  shore 
  edge 
  of 
  this 
  alluvial 
  belt, 
  as 
  has 
  been 
  

  

  already 
  shown, 
  is 
  fringed 
  almost 
  along 
  its 
  entire 
  length 
  by 
  a 
  line 
  of 
  

  

  blown 
  sands 
  of 
  varying 
  width 
  and 
  heiglft. 
  

  

  ( 
  15 
  ) 
  

  

  